1. Field of the Invention
The invention relates to a device and a method for biometric authentication, and more particularly to the biometric authentication device and method which include the image-capturing and detecting the fingerprint and vein images of a user finger for identification.
2. Description of the Prior Art
To ensure security over conventional digital personal identification techniques such as those applying personal identification numbers, digital keys, hardware keys having built-in smart chips and so on, more and more personal identification and security systems are interested in adopting biometric authentication apparatuses, such as the biometric authentication apparatus by judging the fingerprints and/or vein growth under the skin.
In the art, the fingerprint authentication technique can be seen in various Taiwan patents, such as those having the publication numbers 565094, M343215 and 201145179. Yet, in all of those teachings, the identification technique does involve only the identification upon fingerprints. Such a single biometric authentication means obviously provides only limited security protections. Further, in the aforesaid teachings, visible light sources are commonly used and thus inhibited to further detections, for example the investigation through the vein growth of the finger. The foregoing visible light sources are reflective light sources and are projected upward onto the contact surface between the first finger member of user finger and the device so as to generate reflective lights from the contact surface, which is further captured by the device to analyze the fingerprint image. However, though the vein image can be formed by the hemoglobin absorbing lights with specific wavelengths, yet these particular lights with specific wavelengths do not include the visible lights. Furthermore, this conventional fingerprint authentication needs to go through the finger to be depressed substantially onto the contact surface, and such a depression would change the density of the depressed portion on the finger and thus change the original distribution of the veins thereinside. Therefore, it is obvious that the aforesaid authentication method can only be applied to identify the fingerprint, but not relevant to the vein structure inside the first finger member of the tested finger.
In a US patent with a publication number 20090185726, a 4-in-1 imaging apparatus is provided able to recognize an image for authentication of a user in reading the fingerprint, the finger vein, the palm and the palm vein. However, in this disclosure, only two application pairs are included; in which one is the pair of the fingerprint and the finger vein, and another is the pair of the palm and the palm vein. From the teaching, a time-division is performed to control two reflective light sources at different positions for processing the feature identifications. That is to apply a light source to verify the fingerprint and/or the palm, and another light source to verify the finger vein and/or the palm vein. Apparently, in this teaching, one more control circuit is required to share the identifications and thus complicated circuiting design is inevitable.
In two related Taiwan patents with publication numbers M375256 and 201211914, vein identification techniques are taught, respectively. However, a common feature in between is that only the vein authentication technique is provided, and so it is clear that such an identification application is less secured. Further, in M375256, the whole apparatus is too big in occupation for lacking a relevant light guiding mechanism, while, in 201211914, neither an appropriate optical system nor a light guiding mechanism is disclosed.
In a Taiwan patent with a publication number 200947315, a technique to verify both the fingerprint and the finger vein is disclosed. However, in this teaching, major efforts are focused on circuit design and data processing in image and identification verifications, and again neither an appropriate optical system nor a light guiding mechanism is disclosed. Further, in this teaching, 2-D capacitor types of the fingerprint image sensor and the vein image sensor are introduced to perform in order the fingerprint image and the vein image, and it is apparently that such an application can only contribute to a high hardware cost. Also, for two image sensors for different imaging processes are needed in this teachings, thus substantial difficulties and complexities in circuiting and imaging can be foreseen.
In a US patent with a publication number 20110129128, a technique to verify both the fingerprint and the finger vein is also disclosed. In this teaching, major efforts are focused on circuit design and data processing in image and identification verifications, and again neither an appropriate optical system nor a light guiding mechanism is disclosed. Further, in this teaching, a resistance type or a capacitor type of semiconductor sensing plate is introduced to detect the fingerprint, while another image sensor accompanying a light source is to capture and identify the vein image. Obviously, different sensors for imaging the fingerprint and the vein can result in a higher hardware cost and more complicated circuiting for providing two sets of sensors for separate image capturing and data processing.
In all the foregoing teachings, a common shortcoming is noticed. The common shortcoming is to regard the vein authentication method in palm or fingers, in which the feature of the oxygen-deficient hemoglobin in the vein to absorb lights with specific wavelengths is utilized to make possible the image capturing and further analyzing upon the vein by the CMOS or CCD, before a verification upon a user according to his/her biometric can be performed. However, according to the present art, the IR LED is the most popular light source and has a wider spectrum by compared to a laser diode. A wider spectrum for the IR LED implies that part of the lights would be absorbed by the peripheral tissues around the vein and consequently noises would be generated therefrom to further form obstacles for further image analysis. Therefore, by compared to the laser diode as a light source, the IR LED can only obtain an obscure image and thus an improvement thereupon is clear.